Zooplankton
vertical migration and the active transport of carbon and nitrogen in the Sargasso Sea

Debbie Steinberg, Ph.D.
Bermuda Biological Station for Research, Inc.

Wednesday, October 21, 1998
3:00 p.m.Pacific Forum

Transfer of carbon and nutrients from the upper ocean to the deep sea largely results
from biological processes (sinking particles and active transport) and their linkage to
physical processes (mixing of dissolved organic matterDOM). The least known
component of the "biological pump" is the active transport of carbon and
nutrients by diel vertical migration of zooplankton. We measured respiration and excretion
rates of common vertically migrating zooplankton at the Bermuda Atlantic Time-series Study
(BATS) station in the Sargasso Sea. The inclusion of dissolved organic carbon and nitrogen
excretion in this study builds on previous research on active transport of inorganic
carbon and nutrients and allows a direct assessment of the role of zooplankton in the
production of DOM used in midwater microbial processes. Organic excretion represents a
significant augmentation to the vertical flux that has already been documented for
inorganic carbon and nitrogen (CO2 and NH4) flux by migrant
zooplankton. In addition, migratory fluxes are significant compared to other transport
processes (sinking particles and physical mixing of DOM). During most of the year when
deep mixing does not occur, diel migration by zooplankton likely provides an important
supply of DOM to the deeper layers that is available for use by the microbial community.
New estimates of active transport by migrants may help resolve observed imbalances in the
carbon budget at BATS, but the magnitude is highly dependent on the biomass of the
migrating community. Other zooplankton-mediated fluxes (production of fecal pellets,
molting, and mortality at depth) will also be discussed.